Today, we get a radiator for our brains. The University of
Houston's College of Engineering presents this series about the
machines that make our civilization run, and the people whose
ingenuity created them.

Braindance is the odd title of Dean Falk's recent book on
human evolution. She offers new means for dealing with the old
issue of how modern humans finally emerged, some 30,000 years ago.
Falk begins four and a half million years ago with the species
Australopithecus, first discovered in South Africa in 1924.

In those days, paleontologists shied away from controversy
with anti-evolutionists by classifying anything that might be our
ancestor as human. That's how a major anti-evolution myth grew
up -- the myth that we couldn't find the missing link.

Australopithecus did walk on its hind legs. But there its
humanity ends. Its brain was the same size as a chimpanzee's --
about a third the size of yours. Falk believed the brain of that
not-so-missing link was the key to the puzzle.

She found structures in Australopithecus's brain that were
apelike, not human. Here was a creature who walked upright with
hands free for two million years, yet it was endowed with the
brain of an ape. The famous Lucy skeleton was one of these.

Then, a little over two million years ago, our ancestor's
brain began growing. It took on the folds and creases of your
brain or mine. A species called Homo habilis had a forty
percent larger brain. By 1.5 million years ago, Homo erectus was walking
the hot plains of Central Africa with a brain more than double
the size of Australopithecus's -- who was still around, it seems.

Falk struggled to understand what had happened. Then, something
emerged from her subconscious. One day her car mechanic had told
her, "The size of your car's engine is limited by the capacity of its radiator to cool it."
That was it! The brain is terribly sensitive to changes in temperature.
It absolutely must be cooled in summer and heated in winter. But
where is its radiator? Falk began studying the blood supply to ancient brains.

Sure enough: along with changes in brain size ran an evolving
blood delivery system. When Lucy took to her hind legs, her
head had to bear the brunt of the African sun. She began changing,
very slowly. More holes appeared within humanoid skulls to
provide access for more blood to cool the brain. The radiator of
a Model-T evolved into the radiator of your Rolls-Royce brain.

It was 125,000 years ago that our brains reached their full
modern size in, of all people, the Neanderthals. They began
creating art, building huts, burying their dead, and worshipping
deities. They weren't toilet trained, it seems, but then -- if
you look at our lakes and rivers -- maybe we aren't either. But
now we had our radiator and now the real fun was about to begin.

I'm John Lienhard at the University of Houston, where we're
interested in the way inventive minds work.